candv package

candv.base module

This module defines base constant and base container for constants. All other stuff must be derived from them.

Each container has constant_class attribute. It specifies class of constants which will be defined within contaner.

class candv.base.Constant

Bases: object

Base class for all constants. Can be merged into a container instance.

Variables:name (str) – constant’s name. Is set up automatically and is equal to the name of container’s attribute

full_name

merge_into_group(group)

Called automatically by container after group construction.

Note

Redefine this method in all derived classes. Attach all custom attributes and methods to the group here.

Parameters:group – an instance of ConstantsContainer or it’s subclass this constant will be merged into Returns:None

to_group(group_class, **group_members)

Convert a constant into a constants group.

Parameters:

• group_class (class) – a class of group container which will be created
• group_members – unpacked dict which defines group members.

Returns:

a lazy constants group which will be evaluated by container. During group evaluation merge_into_group() will be called.

Example:

from candv import Constants, SimpleConstant

class FOO(Constants):
    A = SimpleConstant()
    B = SimpleConstant().to_group(
        group_class=Constants,
        B2=SimpleConstant(),
        B0=SimpleConstant(),
        B1=SimpleConstant(),
)

class candv.base.ConstantsContainer

Bases: object

Base class for creating constants containers. Each constant defined within container will remember it’s creation order. See an example in constants().

Variables:constant_class – stores a class of constants which can be stored by container. This attribute MUST be set up manually when you define a new container type. Otherwise container will not be initialized. Default: None Raises TypeError:  if you try to create an instance of container. Containers are singletons and they cannot be instantiated. Their attributes must be used directly.

constant_class

Defines a top-level class of constants which can be stored by container

alias of Constant

full_name = 'ConstantsContainer'

name = 'ConstantsContainer'

candv.base.with_constant_class(the_class)

A mixin factory which allows to set constant class for constants container outside container itself. This may help to create more readable container definition, e.g.:

>>> from candv import Constants, SimpleConstant, with_constant_class
>>>
>>> class SomeConstant(SimpleConstant):
...     pass
...
>>> class FOO(with_constant_class(SomeConstant), Constants):
...     A = SomeConstant()
...     B = SomeConstant()
...
>>> FOO.constant_class
<class '__main__.SomeConstant'>

Module contents

This module provides ready-to-use classes for constructing custom constants.

class candv.ValueConstant(value)

Bases: candv.base.Constant

Extended version of SimpleConstant which provides support for storing values of constants.

Parameters:value – a value to attach to constant Variables:value – constant’s value

merge_into_group(group)

Redefines merge_into_group() and adds value attribute to the target group.

class candv.Values

Bases: candv.base.ConstantContainerMixin, candv.base.ConstantsContainer

Constants container which supports getting and filtering constants by their values, listing values of all constants in container.

classmethod filter_by_value(value)

Get all constants which have given value.

Parameters:value – value of the constants to look for Returns:list of all found constants with given value

full_name = 'Values'

classmethod get_by_value(value)

Get constant by its value.

Parameters:value – value of the constant to look for Returns:first found constant with given value Raises ValueError:  if no constant in container has given value

classmethod itervalues()

Same as values() but returns an interator.

Note

Overrides itervalues() since 1.1.2.

name = 'Values'

classmethod values()

List values of all constants in the order they were defined.

Returns:list of values

Example:

>>> from candv import Values, ValueConstant
>>> class FOO(Values):
...     TWO = ValueConstant(2)
...     ONE = ValueConstant(1)
...     SOME = ValueConstant("some string")
...
>>> FOO.values()
[2, 1, 'some string']

Note

Overrides values() since 1.1.2.

class candv.VerboseConstant(verbose_name=None, help_text=None)

Bases: candv.VerboseMixin, candv.base.Constant

Constant with optional verbose name and optional description.

Parameters:

• verbose_name (str) – optional verbose name of the constant
• help_text (str) – optional description of the constant

Variables:

• verbose_name (str) – verbose name of the constant. Default: None
• help_text (str) – verbose description of the constant. Default: None

class candv.VerboseMixin(*args, **kwargs)

Bases: object

Provides support of verbose names and help texts. Must be placed at the left side of non-mixin base classes due to Python’s MRO. Arguments must be passed as kwargs.

Parameters:

• verbose_name (str) – optional verbose name
• help_text (str) – optional description

Example:

class Foo(object):

    def __init__(self, arg1, arg2, kwarg1=None):
        pass


class Bar(VerboseMixin, Foo):

    def __init__(self, arg1, arg2, verbose_name=None, help_text=None, kwarg1=None):
        super(Bar, self).__init__(arg1, arg2, verbose_name=verbose_name, help_text=help_text, kwarg1=kwarg1)

merge_into_group(group)

Redefines merge_into_group() and adds verbose_name and help_text attributes to the target group.

class candv.VerboseValueConstant(value, verbose_name=None, help_text=None)

Bases: candv.VerboseMixin, candv.ValueConstant

A constant which can have both verbose name, help text and a value.

Parameters:

• value – a value to attach to the constant
• verbose_name (str) – optional verbose name of the constant
• help_text (str) – optional description of the constant

Variables:

• value – constant’s value
• verbose_name (str) – verbose name of the constant. Default: None
• help_text (str) – verbose description of the constant. Default: None